MVC BeginCollectionItem 嵌套列表索引不起作用

Question

I've got a BeginCollectionItem repeater that is working perfectly, however when I try and follow the Joe Stevens blog to add nested lists it doesn't work in the way I expected.

I've used the BeginCollectionItemCore as I'm using AspNetCore, I've taken the code from here as it says it has the built in elements from the blog already in there: https://github.com/saad749/BeginCollectionItemCore

I have a main BeginCollectionItem called Section and a nested collection called SingleLine. I expected the code to output something like: Section[long-code-here].SingleLine[another-code-here].SingleLineTextBlock however what I get is SingleLine[long-code-here].SingleLineTextBlock

I've included my code below;

Model:

namespace project.Models.SetupViewModels
{
    public class SOPTopTemplateBuilderViewModel
    {
        public List<SectionViewModel> Section { get; set; }
    }
    public class SectionViewModel {
        public int SectionId { get; set; }
        public string SectionText { get; set; }
        public string TopTempId { get; set; }
        public List<SingleLineViewModel> SingleLines { get; set; }
    }
}

Partial view:

@model project.Models.SetupViewModels.SectionViewModel
@using HtmlHelpers.BeginCollectionItemCore
<div class="new-section form-row">
    @using (Html.BeginCollectionItem("Section"))
    {
    <div class="top-line">
        <div class="col-12 col-md-11">
             @Html.HiddenFor(m => m.SectionId, new { @class="id" })
             @Html.EditorFor(m => m.SectionText, new { @class = "form-control limit-form"})
         </div>
        <div class="col-12 col-md-1">
        </div>
    </div>
    }
    <div class="main-row">
        <div class="buttons-div">
            <button id="add-single-line" type="button" data-containerPrefix="@ViewData["ContainerPrefix"]">Add Single Text</button>
        </div>
    </div>
    <div class="main-row">

    </div>
</div>

Ajax to add new line:

var form = $('form');
var recipients = $('.main-row');
$("#add-single-line").click(function(){
     $.ajax({
        type: "POST", 
        url: '@Url.Action("GetNewSingleLine")',
        data: { "containerPrefix": recipients.data("containerPrefix") },
        success: function (data) {
            recipients.append(data);  
        }
     });  
});

EditorFor:

@model project.Models.SetupViewModels.SingleLineViewModel
@using HtmlHelpers.BeginCollectionItemCore
@using (Html.BeginCollectionItem("SingleLine"))
{
    <div class="single-line-row">
        @Html.HiddenFor(m => m.SingleLinkTextID, new { @class="id" })
        @Html.TextBoxFor(m => m.SingleLinkTextBlock, new { @class = "form-control limit-form"})
   </div>
}

EditFor Controller:

public ActionResult GetNewSingleLine(string containerPrefix)
{
   ViewData["ContainerPrefix"] = containerPrefix;
   return PartialView("SingleLineViewModel", new SingleLineViewModel());
}

Answer 1

I struggled with this exact issue for a while until I happened upon this post - which ended up leading me to an answer (thank you!). In the example above, it is storing the prefix in the button.add-single-line but attempting to load it from the div.main-row so you probably are getting 'undefined' as the prefix. By pulling from the same item which cached the value, the code above will do what is intended.